1. Field of the Invention
The present invention relates to a thin-film magnetic head for reading and writing data signals, a head gimbal assembly (HGA) with the thin-film magnetic head and a magnetic recording apparatus with the HGA. Especially, the present invention relates to a thin-film magnetic head for writing data signals by a heat-assisted perpendicular magnetic recording technique using a near-field light, an HGA with the thin-film magnetic head and a magnetic recording apparatus with the HGA.
2. Description of the Related Art
Recently, in a magnetic recording apparatus such as a magnetic disk drive apparatus, a thin-film magnetic head is strongly required to further improve its performance because the recording density of the apparatus becomes higher due to the spread use of data with larger volume. As the thin-film magnetic head, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) effect element for reading data signals from a magnetic recording medium such as a magnetic disk and an electromagnetic coil element for writing data signals to the magnetic recording medium.
The magnetic recording medium has a magnetically discontinuous layer where magnetic microparticles are gathered together. Usually, each of the magnetic microparticles has a single magnetic-domain structure, and one recording bit consists of a plurality of the magnetic microparticles. Therefore, for improving the recording density, irregularity in the boundary of the recording bit must be reduced by decreasing the size (volume) of the magnetic microparticle. However, a problem is likely to occur that the size decrease causes thermal stability of the magnetization of the recording bit to be degraded.
A guide of the thermal stability of the magnetization is given as KUV/kBT, where KU is a magnetic anisotropy energy in the microparticle, V is a volume of a single microparticle, kB is Boltzmann constant and T is absolute temperature. Decreasing the size of the microparticle is equivalent to decreasing the volume V. Therefore, when the size is decreased, the thermal stability is degraded due to degrease in the KUV/KBT value. As a measure of the thermal stability problem, it may be possible that the KU is increased concurrently. However, the increase in the KU causes the increase in coercive force of the magnetic recording medium. On the other hand, the write field intensity of the magnetic head for writing data signals against the coercive force is limited by the amount of the saturation magnetic flux density of the soft-magnetic pole material of the head. Therefore, the head cannot write data signals to the medium when the coercive force exceeds the write field limit.
As the first method for solving the thermal stability problem, a perpendicular magnetic recording technique may be adopted instead of the conventional longitudinal magnetic recording technique. The thickness of the recording layer in the perpendicular magnetic recording medium can be increased more sufficiently than conventional. As a result, the thermal stability can be improved due to the larger volume V with the larger thickness.
As the second method, a patterned media may be considered as a candidate. While one recording bit consists of N pieces of the magnetic microparticles in the conventional magnetic recording as described above, one recording bit is a single pattern region with volume NV in the patterned media. As a result, the value of the guide of the thermal stability becomes KUNV/KBT, which means high improvement of the thermal stability.
As the third method for solving the thermal stability problem, a heat-assisted magnetic recording technique is proposed, in which the magnetic head writes data signals to the magnetic recording medium formed of a material with the large KU value, by reducing the coercive force of the medium with heat supplied to the medium just before the write field is applied. The heat-assisted magnetic recording technique has some similarity to a magnetooptic recording technique, however, obtains a spatial resolution corresponding to an applied magnetic field region, while the magnetooptic recording technique obtains a spatial resolution corresponding to an emitted light spot.
As a proposed heat-assisted magnetic recording, Japanese patent Publication No. 2001-255254A describes a light recording technique utilizing a near-field light probe that has a metal scatterer with strobilus shape formed on a substrate and a dielectric material film formed around the metal scatterer. And Japanese patent Publication No. 10-162444A describes a technique in which a head provided with a solid immersion lens writes ultrafine domains on a magnetooptical disk using a micro light spot. Further, U.S. Pat. No. 7,042,810 describes a heat-assisted technique in which an internal laser element emits a light to an optical fine aperture opposed to a medium.
Further, Japanese patent Publication No. 2004-158067A describes a scatterer as a near-field light probe, which is formed in contact with the main magnetic pole of a head for a perpendicular magnetic recording in such a way that the irradiated surface of the scatterer is perpendicular to the surface of the medium. And U.S. Pat. No. 6,674,594 describes the relation between the pole width WW of a recording head element and the width TWW of the area heated by a laser semiconductor in a recording and reproducing head having the laser semiconductor.
Furthermore, IEEE Transactions on Magnetics, Vol. 41, No. 10, pp. 2817-2821, 2005 describes a technique in which a recording pattern with the track width of approximately 70 nm is formed by using a near-field light and a magnetic field generated from a U-shaped near-field light probe formed on a quartz crystal slider. And Journal of the Magnetics Society of Japan, Vol. 29, No. 1, pp. 5-13, 2005 describes a photoheating element having a grating in which a transmitting diffraction grating is butted to be joined to a hardly-transmitting diffraction grating. Further, as examples of using an optic fiber, Japanese patent Publication No. 2000-173093A describes a structure in which a metal film with a pinhole is formed on an obliquely cut surface of an optic fiber. And U.S. Pat. No. 6,044,056 describes an optical flying head having a movable mirror for directing a laser light from an optic fiber to an optical lens system.
In the above-described techniques, the method of heating the medium by using a near-field light generated from a near-field-light-generating means that is irradiated with laser light from the optic fiber, etc. is considered as a promising technique because a fine near-field light having a required intensity can be obtained with comparative ease.
However, in these techniques, there is some possibility of writing error such as an insufficient writing to a desired track or an unwanted writing or erasing to the adjacent tracks, depending on the range and timing of the near-field light application during heat-assisting operation.
Actually, the end of the near-field-light-generating means reaches the head end surface opposed to a magnetic recording medium to heat the medium. Depending on the position and shape of the reaching end, there are some cases to miss sufficient writing to a track to be written because of insufficient heating of the track. Further, when writing at rather intervals after applying the near-field light, the coercive force of the medium may exceed the writing limit of the write field due to the cooldown of the medium. In this case, a desired writing cannot be performed. Furthermore, in the case that the near-field light covers the adjacent tracks, an unwanted writing may be performed on the adjacent tracks. However, in the past, no clear and adequate measures against these problems have been suggested.
Meanwhile, in the above-described thin-film magnetic head for perpendicular magnetic recording, the shape on the head end surface of the main magnetic pole is set to be a trapezoid with a longer edge on the trailing side. That is to say, the both side surfaces of the end of the magnetic pole have a bevel angle for avoiding unwanted writing and erasing to the adjacent tracks due to a skew angle derived from driving of a rotary actuator. However, in the case that the head for perpendicular magnetic recording is provided with the near-field-light-generating means, the near-field light has some possibility to cover the adjacent tracks under the influence of the skew angle, depending on the position and shape of the end of the near-field-light-generating means. Therefore, depending on the position and shape of the end of the main magnetic pole, an unwanted writing or erasing may be performed to the adjacent tracks.
As a measure against this problem, the above-described U.S. Pat. No. 6,674,594 describes a technique adjusting the relation between the width WW of a magnetic pole of a write head element and the width TWW of the area heated by a laser source to suppress the following deviance of the write head element to a read head element. However, this technique is not intended for a thin-film magnetic head with a main magnetic pole for perpendicular magnetic recording. Thus, in the past, no clear and adequate measures against this problem have been suggested.